Posted By
crock
on 2021-02-28
14:56:15
 |  Re: Plus/4 issues trying to solve with Diag264
From what you describe, I would be looking for a physical fault such as a dry joint, flaky socket, or solder bridge. The pattern implies D6 is stuck high which, as you say, is facilitated by U17.
If D6 was being pulled high on the whole databus, the CPU would not be able to read ROM's correctly, so it is most likely RAM related, and if you're sure the chip you replaced it with is good, I would be looking for physical defect.
Rob
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